[Users] Claws "hangs" with 100% CPU

[claws at my-mail-box.net]

I observe the following behavior: occasionally,
when opening a minimized Claws window, the empty
window frame will appear, but the content of the
window (the actual Claws UI) will not appear.

When this happens, the Claws process is using 
100% CPU (on a single core). Looking at past CPU
utilization, I can see that the "100%" started
long BEFORE I tried to open the window.

The process "hangs", and does not "come back" in
any meaningful time. The process cannot simply be 
killed, but must be killed with "kill -9".

Observing the system, I am quite sure that Claws is
not just "busy" doing something useful, but "hangs",
indefinitely.

Claws does not write anything relevant to the console. 

In the past, I used to observe this behavior quite
rarely (maybe every other month), but since upgrading
to Linux Mint 21 Vanessa and Claws 4.0.0 it has become
very frequent: at least once a week, sometimes more
often. (Which is beyond the pain point, hence this
report.)

My Claws client talks to a local IMAP server and
several remote POP servers. The IMAP server seems
ok, even when this happens. The POP servers are ok,
at least once I killed (-9) Claws and logged in to
them all again.

I realize that these are not terribly detailed 
diagnostics. What more can I do to track this
issue down?

I have seen a few vaguely similar reports (hanging
with 100% CPU), but I don't recall seeing any 
resolution. What can we do to track this down?

Best,

		Ph.